SSMA and SMA RF Connectors – Center Contact Retention

Comments off 5884 Views5

Most RF connectors require some form of internal component captivation to ensure proper mechanical integrity. The design must strike a balance with electrical performance which can be difficult to achieve with higher frequency connectors.

Epoxy and mechanical are common methods of captivation that are governed by military and industry specifications. SMA series connectors cover a wide range of captivation methods and are high frequency, average in size and very popular in the RF/microwave industry. SMA specifications per M39012 is 6 pounds axial (direct force in pounds) and 4 inch-ounces radial (torque). All SMA’s have an axial requirement but many do not have a radial. Other RF connector series have similar specifications.



Mainly for receptacles with tabs, slots, blunt posts and solder cups that are soldered onto a PC board. Epoxy is the preferred method when any axial or rotational movement of the center contact may break the PCB solder joint. Silver epoxy fill will improve RF leakage.

Axial – 6 lbs | Radial – 4 inch-ounces

VSWR: Very Good | RF Leakage: -60 dB




Adapters, Field Replaceables and similar designs where radial movement is allowed. These connectors do not have a soldering requirement of the center contact. There are many variations of barb captivation and epoxy is sometimes used.

Axial: 6 lbs | Radial: None

VSWR: Good | RF Leakage: -75 to -100 dB


knurlMechanical (Barb/Knurl)

For applications that require radial captivation and low cost. This design, along with other types of enhanced mechanical captivation such as staked and special barbs have poor VSWR performance due to the excessive capacitance introduced.

Axial – 6 lbs | Radial – 4 inch-ounces

VSWR – Average to Poor | RF Leakage: -75 to -100 dB



shoulderCable Connectors

In most cases, the cable center conductor will support the soldered connector’s center contact. Small connectors and cable commonly use a shoulder design that butts two insulators against the center contact. Epoxy may be used on assemblies with very small cable. Mainly used in low frequency applications.



Other areas of captivation include “snap-in” contacts called out in some MIL specifications and precision (metrology grade) connectors that use a noryl-PPO tm or rexolite bead to support and captivate an airline.

Choosing a company that is committed to the performance you expect is critical in any successful RF coaxial endeavor. Coaxicom is known for excellent performance standards and stand behind our products with exceptional quality and customer service.

Coaxial Components Corp is a woman-owned small business and ISO 9001:2015 / AS9100D certified manufacturing facility that ships same day from a broad inventory of microwave and RF products.,, 866-COAXICOM (866-262-9426)

Sign up here for your complimentary welcome package!